Scanning electrochemical microscopy and video microscopy investigations of Tiron-mediated polypyrrole nucleation on AA2024-T3

Scanning electrochemical microscopy (SECM) and video microscopy have been used to examine the mediated electrodeposition of polypyrrole on AA2024-T3. Of particular interest is the role of surface heterogeneity (namely, copper-rich secondary phase particles) on electrodeposition mediated by 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron). SECM shows that polymer nucleation occurs exclusively on the aluminum matrix of the alloy. Video microscopy shows this to be true on a model alloy (a pure Al substrate with an embedded Cu wire) as well, and also suggests that polymer growth is directional toward the copper-rich sites in the absence of sulfate in the deposition solution. A model is presented in which polymer deposition on the copper-rich sites is inhibited either by CuSO₄-induced passivation or by the loss of mediator due to Cu–Tiron complex formation.